Chapter 113 Why are we all problems in front of Director Gao? (3k)

Gao Zhendong had not expected the arrival of the comrades from the Carbon Research Institute. As far as he knew in his previous life, the first generation of SRM rocket throat lining materials of the Carbon Research Institute was developed in the early 60s. There should be certain results by now. The Guidance Research Institute can just ask the Northeast Carbon Research Institute for the results directly.

The throat liner of the first generation SRM rocket was copied from the C-17δ graphite of the Russians in the north. Its performance was average, but it was usable and was successfully used on the launch vehicle of the first domestically-produced satellite.

But I didn't expect them to come to me. Logically speaking, the Carbon Research Institute is much more professional than me in this regard.

But no matter what, since we are here, we might as well make the best of it. It’s also good to have some communication.

After a few words, the conversation between the two sides got down to business.

Zeng Gong’s classmate’s surname is Duan, and he is also the leader of this team, so the communication is mainly done by him and Gao Zhendong.

"Director Gao, I heard from Lao Zeng that when you were communicating with them about missile nozzles last time, you mentioned polycrystalline graphite infiltrated with silicon?"

Gao Zhendong said: "That's true. Are you doing siliconization of polycrystalline graphite?"

"Yes, Director Gao, we are indeed doing silicon infiltration of polycrystalline graphite to increase the strength of graphite, but the effect is not satisfactory."

Gao Zhendong thought about it, but didn't know what to say. These units, including himself, were all confidential, so he had to try to ask, "Duan Gong, can you tell me?"

Duan Gong came here this time, well prepared. The red lines had already been drawn in the unit, and the object to be imitated was C-17δ, which was someone else's product, so there was a lot to say.

"It's not inconvenient. We are here to ask for help. If you don't tell me this or that, it will be difficult for you, Director Gao."

Mr. Duan took out a document and turned to a picture, which was an enlarged image of the graphite surface, and there were some data tables next to it.

"Director Gao, look, this is the material test record after our siliconization. The thermal cracking phenomenon is very serious and the strength is not good."

Gao Zhendong carefully observed Duan Gong's pictures and data records. To be honest, he didn't know much about this stuff, but he was bored in his previous life, and read a lot of papers in order to communicate with people on the forum.

In order to compete with others, he even spent his own money to buy the necessary papers on various knowledge websites. So boredom is a terrible thing. It will damage your spirit and impact your wallet.

Gao Zhendong looked at Duan Gong's information, holding his chin with his hand, and did not speak for a long time. This made the people in the Carbon Research Institute think that he was thinking, analyzing, and summarizing, but in fact he was just recalling.

After a while, Gao Zhendong asked, "Mr. Duan, can you tell me about your siliconization method?"

Gao Zhendong has seen methods for siliconizing polycrystalline graphite, including liquid phase siliconizing method, in-situ reaction method, dip coating method, chemical vapor deposition method, hot pressing sintering method, reactive melt infiltration method, etc. He first needs to know what method Duan Gong and his team are using.

Mr. Duan did not hide anything and explained the siliconizing method used in his unit.

Gao Zhendong listened carefully and felt that it was a bit like the in-situ reaction method, but it might be in the Carbon Research Institute and it is not called that name now.

He didn't bother with the name and asked, "Is alumina added to the carburizing material?"

Duan Gong was delighted when he heard this. The fact that he could ask this question proved that Director Gao really understood graphite siliconization. He nodded and said, "Yes, it was added. As a sintering aid, the addition of alumina can refine the silicon carbide grains and make the silicon carbide layer denser."

Gao Zhendong did not comment, and then asked: "What is the size of the carbon particles?"

"0.xx mm, high density."

Gao Zhendong asked, "Are you considering that small-particle, high-density carbon raw materials can increase density and strength?"

Duan Gong nodded: "Director Gao is right, that's what I think."

After asking a few more questions, Gao Zhendong organized the papers he had read in his head and said with a smile: "Mr. Duan, I have a few suggestions that you can consider appropriately."

Mr. Duan was overjoyed and actually had several suggestions. He thought the trip was not in vain: "Director Gao, please tell me what you think."

"The siliconization method you used is indeed not the most suitable method for this situation. With this method, the siliconized graphite silicon carbide layer has a large number of pores, and the SiC particles are loosely stacked, so the strength is naturally not very good."

"At the same time, with your method, once the concentration of silicon carbide in liquid silicon reaches saturation, it will grow rapidly and eventually form a thicker silicon carbide layer on the surface of the graphite matrix."

Why is Gao Zhendong so sure? Because he had seen the SEM (scanning electron microscope) and XRD (X-ray diffraction) results of the products of this method in his previous papers. Both technologies can observe the microstructure of the sample. There is no doubt that the current Carbon Research Institute does not have this condition.

Hearing that Gao Zhendong had found the problem, Duan Gong was first happy, then worried. It was not enough to just find the problem. "Director Gao, what method should we use?" Gao Zhendong said, "My suggestion is to use liquid phase siliconization. In my opinion, this method is the same as the method you are using now. It has the advantages of simple operation, low equipment cost, and suitability for mass production. Compared with other methods, this method can also retain the graphite matrix to a greater extent, which is conducive to maintaining the self-lubricating and thermal conductivity of graphite."

"But the biggest difference between it and the method you are using now is that the silicon carbide in its silicified graphite mainly exists in the graphite gaps, rather than a thicker silicon carbide layer on the surface of the silicified graphite like the method you are using. This thicker silicon carbide layer should be the culprit for the serious thermal cracking."

Gao Zhendong has a basis for this statement. In a public paper on domestic SRM materials, it was mentioned that the biggest problem to be solved in the process of imitating C-17δ was the thermal cracking problem caused by the excessive thickness of the silicon-infiltrated layer, but it did not say what means were used.

In Gao Zhendong's opinion, the solution he proposed should be able to solve this problem, as different approaches lead to the same result.

Duan Gong was overjoyed when he heard this. An expert can tell whether something is good or not with just one demonstration. These few words hit the nail on the head. When he heard that there was really a new process method, he immediately asked, "Director Gao, how exactly is this liquid phase siliconization method you mentioned done?"

Gao Zhendong was not shy about his answer: "Silicon carbide and silicon are mixed in a ratio of 3:2 as the silicon source material, the reaction temperature is 1600°C, and the reaction is carried out in a vacuum environment for 0.5 hours. See, isn't it simple?"

After hearing this, Duan Gong almost threw his stick at him and said, "Yes, yes, yes, you are right, it is very simple."

But think about it, this method is really simple. I can’t even think of anything simpler than this. If it is effective, that would be great. The cost is really low.

Gao Zhendong did not give Duan Gong a chance to throw his pen, and continued: "This way, we can also solve your second problem, the use of alumina."

"Alumina?"

"That's right. Although aluminum oxide can theoretically refine SiC grains and make the silicon carbide layer denser, in reality, when there is an excess of aluminum oxide, the reaction will produce a large amount of gas. When these gases escape, they will destroy the density of the silicon carbide layer and have an adverse effect on the performance of the silicified graphite, which will also reduce the performance of your finished product."

Now the people at the Carbon Research Institute understood that Director Gao was a real master. The other technical staff at the Carbon Research Institute had stars in their eyes as they watched the two big guys communicate, writing quickly.

Gao Zhendong's next words made the people at the Carbon Research Institute feel a little embarrassed: "Next, let me talk about the third question."

Ah, are there so many problems with our technology? There are problems everywhere. This is the third one. I am so ashamed.

Duan Gong looked ashamed: "Director Gao, please continue."

Gao Zhendong pointed to the carbon particle parameters on the record and said, "I suggest you increase the diameter of the carbon particles a little bit, to 1.x millimeters. At the same time, don't use compact, high-density carbon particles, use looser ones."

A bunch of technicians at the Carbon Research Institute had questions in their minds, but they didn't dare to speak up. It was Duan Gong who asked: "Wouldn't this reduce the density and strength?"

Gao Zhendong shook his head: "Not really. You have to consider that the liquid phase siliconization method generates silicified graphite inside the graphite. These loose gaps are just the best place for silicon carbide to stay, which is conducive to the uniform distribution of silicified graphite in the product. In addition, the reduction of graphite particle size will weaken the overall strength of the product, increase wear and tear, and increase the wear rate."

Needless to say, the people at the Carbon Research Institute were very excited after hearing Gao Zhendong's words.

Each of Director Gao's suggestions sounded well-reasoned and to the point, and the solutions were also clear. These solutions even reduced difficulty and reduced costs.

Although there have been no tests yet, we cannot say that what Director Gao said is correct, but at least in the eyes of the people at the Carbon Research Institute, the chances are very high.

There is a path to follow, which is much more comfortable than groping in the dark.

After recording Gao Zhendong's words, Duan Gong said embarrassedly, "Director Gao, let me ask you another question. Last time, I think you mentioned graphite infiltration into copper?"

Gao Zhendong smiled. He knew why Duan Gong felt embarrassed. He felt that they had taken away all of Gao Zhendong's achievements.

In fact, Gao Zhendong doesn't care about this. He has a lot of things in his head and those he got from the lottery. If he waits for them to be realized one by one, it would be like moving mountains like Yugong. It would be better to take them out and let capable and talented people to come up with them.

He nodded. "Yes, that's right. I did say that. Graphite copper infiltration can not only be used alone, but also in combination with silicon infiltration. Silicon infiltration increases strength, and copper infiltration increases heat resistance. For the material you have now, you can first siliconize it and then copper infiltrate it to further improve the ablation resistance."

Later, someone did a study, using the first type of SRM material mentioned above, after siliconizing it and then copperizing it, the ablation rate of this material could be reduced by about 30%. The effect was very obvious. Although it still could not reach the performance of domestically produced second- and third-generation graphite throat liners, it was already a big surprise for now.

Hearing this, Duan Gong was very surprised and asked carefully: "Then Director Gao, can you..."

　All the statements about the Carbon Research Institute's graphite silicon infiltration and copper infiltration process are nonsense.

Chapter 2 Today

　
(End of this chapter)